Pearlescent pigments are known. An example includes a substrate such as mica coated with a metal oxide having a high refractive index such as titanium dioxide or the like on the surface thereof.
Recently, a pearlescent pigment using plate-shaped alumina as a substrate to improve surface smoothness, heat resistance, and transparency which are defects of mica, has been disclosed (Japanese Patent Laid-Open Publication No. 1997-255891).
However, the method disclosed in the patent specification may not provide a pigment having a satisfactory brightness when the substrate is plate-shaped alumina produced by a hydrothermal method. In this case, adherence of metal oxide particle to the plate-shaped alumina can be significantly deteriorated, and the metal oxide can coagulate to form a large coagulated particle.
In addition, even if the metal oxide particle adheres to the plate-shaped alumina, the particle size of metal oxide coated on the substrate is large, and it can be difficult to provide a silky pearlescent gloss having uniform brightness without particle texture, so that the decorative effect required in various fields may not be satisfactory.
In addition to the above method which attempts to improve the inherent properties of the pearlescent pigment, there have also been efforts to prevent flow marks or weld lines when injection molding a thermoplastic resin composition including a pearlescent pigment. Such efforts, however, have met with limited success.